A scheme for utilizing multiple antennas, such as multiple-input multiple-output (MIMO) system, has been developed. By utilizing multiple transmit and receive antennas, a capacity and throughput of the wireless communication system can be enhanced. The performance enhancement is restricted as a correlation of the signals between the plurality of antennas becomes higher. If the correlation of antennas is high, the advantage of a multiple antenna system may be lost.
In a MIMO system, data is converted to a plurality of parallel data streams and the parallel data streams are transmitted simultaneously from different antennas. The data stream may be transmitted only from a subset of the antennas. Selection of antennas for transmission is often based on quality of the link seen at the antenna or other relevant quality indicators. The performance of the MIMO system degrades as signals become more correlated between antenna transmissions.
In general, the antenna correlation depends on factors such as distance between the antennas and channel state including scatterings conditions. Signals received at the receiver are subject to multipath fading and the antenna correlation becomes lower as the influence of fading differs each other. Therefore, it is desirable to lower the antenna correlation in wireless communication systems utilizing multiple antennas.